Development of a spot test system will provide a simple, economical and quick system in eukaryotes for the detection and evaluation of the mutagenic activity of chemical agents in the human environment. Such development of a spot test system involves two steps. The first step is to establish the optimal test conditions in Neurospora crassa and the second step is to find the tester strains which can best detect several different types of genetic alterations. We have established optimal conditions for the spot test and have selected 8 strains from hundreds of mutants as preliminary tester strains. The mutagenicity of MNNG, ICR-170, 4NQO, AF-2, SQ18506, EMS, EI, BP, FANFT, H-193, N-acetoxy-AAF and N-hydroxy-AAF can all be detected by this simple test system.